Bill Gates is putting pressure on the Obama administration to prevent major US energy companies from neutering legislation aimed at stamping out corruption in developing countries.

The billionaire philanthropist has published a letter to the Securities and Exchange Commission, the US financial watchdog, expressing concern at attempts to water down a new law designed to increase transparency in deals involving extractive industries. The former Microsoft chief said it was important that the US was the standard bearer in the fight against corruption, adding: "I feel it is critical to ensure the final rules for this provision are strong and robust and in keeping with the intentions of Congress."

Sources close to Gates said it was unusual for him to make direct appeals, but there was concern about a lobbying campaign in Washington that would provide the big energy companies with loopholes that would allow them to continue operating in their current fashion.

Gates said Africa's natural resources were worth $246bn in exports in 2009, six times greater than the money it received in aid. "Little of this value remained in Africa. Transparency of financial flows is critical to ensuring these valuable resources are transformed into public benefits."

He added that Congress had made clear its intention to make transactions by big American mining and energy companies in developing countries more transparent, adding that the SEC had a "mandate to implement final rules reflecting the clear intent and reporting requirements established by Congress".

Jamie Drummond, the executive director of ONE, the development campaign group, said: "Some of the biggest and richest oil, gas and mining companies are aggressively lobbying against legally binding measures that would help some of the poorest people in the world fight corruption and promote openness. These same companies claim to support transparency.

"The devil is in the detail. Companies are lobbying for technical exemptions so they need not provide information that could actually help citizens fighting corruption at a grassroots level. They are pushing to remove project-level disclosure and keep secret all payments below $1m which will make this data irrelevant for local communities and defeat the point of the legislation.

"They are even arguing that their payments to some of the most opaque governments should be excluded entirely. If this exemption is included it will create a huge perverse incentive for governments to pass new secrecy laws."